Transposition of muscles with their intact neurovascular bundles is a well-accepted procedure in the adult with a predictable outcome. The fate of transposed immature muscle, however, has not been studied. For this reason, muscles were transposed in three 6-week-old puppies and harvested when the puppies were 6 months old. The developing normal and transposed muscles were studied using serial biopsies, electromyography, and histochemical methods, and the growth in bulk was assessed by serial radiography and measurements of length, breadth, height, and weight of the muscles at death. As judged by these criteria, the transposed muscle developed normally. A patient with prune-belly syndrome, treated by muscle transpositions from thigh to abdomen with satisfactory results, is also described.